Which physicist visited Mount Wilson Observatory in 1931 and met Edwin Hubble?

The physicist who visited Mount Wilson Observatory in 1931 and met Edwin Hubble was Albert Einstein. The meeting came as Einstein was reassessing what general relativity implied about the universe.

Einstein’s equations had suggested that the universe could not remain static: it should either expand or contract. To preserve a static cosmos, he had introduced the cosmological constant. Hubble’s observations of galaxy redshifts and their relationship to distance supplied important observational evidence that the universe was expanding, although Georges Lemaître had developed related theoretical and observational work earlier.

During Einstein’s 1931 visit, the astronomers discussed the expanding-universe question at Mount Wilson. Einstein later became associated with the remark that changing his equations had been his “biggest blunder,” though the wording and context are often simplified in popular accounts. The other choices were major physicists, but none is the figure identified in this Mount Wilson episode. The visit also helped cement Hubble’s public reputation as a leading observational cosmologist.